CYTOTOXIC ACTIVITY OF GRAFT-INFILTRATING LYMPHOCYTES CORRELATES WITH CELLULAR REJECTION IN CARDIAC TRANSPLANT PATIENTS

Lymphocytes propagated from allografts have shown a wide spectrum of activity during rejection including cytotoxicity, proliferation, and lymphokine production. It is necessary to correlate these activities to the rejection process to understand the in vivo immune response. The frequent need to obtain a biopsy of human cardiac allografts permits the evaluation of the function of the graft-infiltrating lymphocytes (GIL) as related to development of the rejection process. Lymphocyte cultures established from biopsies taken before, during, and after rejection episodes of grade 1.0 or greater were assayed for surface antigen expression using flow cytometry, proliferative activity using a primed lymphocyte test (PLT), and cytotoxicity using a cell-mediated lympholysis assay. Fifteen rejection episodes were followed from 10 patients. Two patients were followed through two different rejection episodes and one patient through four rejection episodes. CD8+ cells usually predominated during the rejection episode. Following the rejection episodes the GIL showed a shift toward higher proportion of CD4+ cells. Most cultures taken prior to and during rejection episodes (8/9 and 12/13 assayed, respectively) demonstrated > 30% killing of targets bearing donor-related HLA antigens. Seven of 15 cultures remained cytotoxic after a rejection episode whereas 8 of 15 lost cytotoxicity. The patients whose cultures remained cytotoxic after a rejection episode went on to further rejection episodes at 6, 7, 11, 20, 37, or 118 days later. Those patients whose cultures were no longer cytotoxic did not experience any subsequent rejection episode until at least 257 days later. Persistence of alloreactivity, as indicated by the ability to proliferate in a PLT, did not predict future rejection episodes. These results suggest that the cytotoxic activity of the interleukin-2 responsive T lymphocytes in the biopsies is closely related to clinical rejection, and continued cytotoxicity may be a useful prognostic indicator of future rejection episodes.